This invention relates generally to catalyst compounds and, more specifically to the preparation and characterization of Cuxe2x80x94Alxe2x80x94O catalysts to replace Cu/Cr catalysts in specific applications.
The commercial catalysts for hydrogenolysis of carbonyl groups in organic compounds have been dominated by Adkins"" catalyst since the 1930""s (H. Adkins, R. Connor, and K. Folkers, U.S. Pat. No. 2,091,800 (1931)). The Adkins"" catalyst is a complex mixture of primarily copper oxide and copper chromite. The catalyst is used in hydrogenolysis reactions, for example the catalytic hydrogenolysis of an ester to alcohols, illustrated generally by the following reaction: 
Under reaction conditions it is believed that the catalyst reduces to a mixture of metal copper, cuprous oxide and copper chromite. One of the crucial roles of chrome in Cu/Cr catalysts is that it behaves as a structural promoter.
The Cu/Cr catalysts have widespread commercial and industrial application in such diverse processes as hydrogenation of aldehyde in oxoalcohol finishing, hydration of acrylonitrile, fatty acid hydrogenolysis, hydrogenolysis of methyl esters, reductive amination, and a myriad of other hydrogenation and oxidation reactions such as are listed below. U.S. Pat. No. 3,935,128, to Fein et al, provides a process for producing a copper chromite catalyst. U.S. Pat. No. 4,982,020 to Carduck et al., discloses a process for direct hydrogenation of glyceride oils where the reaction is carried out over a catalyst containing copper, chromium, barium and/or other transition metals in the form of oxides which, after calcination, form the catalyst mass. U.S. Pat. No. 4,450,245 to Adair et al., provides a catalyst support wherein the catalyst is employed in the low temperature oxidation of carbon monoxide, another important application of such catalysts.
Environmental issues involving disposal of chrome-containing catalysts, however, are expected to eventually eliminate their use in many countries. Additionally, catalyst activity is one of the most important factors determining a catalyst""s performance. It is, therefore, advantageous to employ non-chrome, copper-containing catalysts having good catalyst activity to replace currently used Cu/Cr catalysts in hydrogenation, alkylation and other reactions.
Several prior art, non-chrome containing catalysts are known. For example, U.S. Pat. No. 5,418,201, to Roberts et al., discloses hydrogenation catalysts in powdered form and method of preparing a hydrogenation catalysts comprising oxides of copper, iron, aluminum and magnesium. U.S. Pat. No. 5,243,095 also to Roberts et al. provides for the use of such copper, iron, aluminum and magnesium catalysts in hydrogenation conditions.
U.S. Pat. No. 4,252,689 to Bunji Miya, describes a method of preparing a copper-iron-alumina catalyst used in hydrogenation. U.S. Pat. No. 4,278,567 to Bunji Miya et al., discloses a similar process for making a copper-iron-aluminum catalyst. U.S. Pat. No. 4,551,444 to Fan-Nan Lin et al., provides a five-component catalyst wherein the essential components are copper, an iron group component, a component of elements 23-26, an alkali metal compound and a precious metal compound.
C. W. Glankler, Nitrogen Derivatives (Secondary and Tertiary Amines, Quarternary Salts, Diamines, Imidazolines), J Am. Oil Chemists"" Soc., November 1979 (Vol 56), pages 802A-805A, shows that a copper-chromium catalyst is used to retain coarbon to carbon unsaturation in the preparation of nitrogen derivatives. U.S. Pat. No. 4,977,123 to Maria Flytzani Stephanopoulos et al., discloses extruded sorbent compositions having mixed oxide components of copper oxide, iron oxide, and alumina. U.S. Pat. No. 3,865,753, to Broecker et al, provides a process for preparing a nickel magnesium aluminum catalyst used for the cracking of hydrocarbons. The prior art, non-chrome containing catalysts have several disadvantages that limit the industrial applicability of the catalysts.
An ideal catalyst should be both chemically and physically stable. Chemical stability is demonstrated by consistent catalyst activity in an acceptable time period. Physical stability is demonstrated by maintaining a stable particle size or physical form during the chemical reaction. Moreover, an ideal catalyst would have narrow particle distribution since particle size affects filtration speed in a commercial process employing the catalysts. The stability is further demonstrated by resistance to common poisons such as sulfur compounds, organic chlorines, bromine and iodine compounds. Generally, stability is tested using Cu/Cr catalyst as the standard catalyst.
An ideal catalyst also would have a low percentage of leachable cations. This ensures the maintenance of catalyst activity and a good product quality.
Furthermore, it is important the catalyst function well in commercial applications. For example, the hydration of acrylonitrile to acrylamide over a copper-containing catalyst is an important industrial application. Several different copper catalysts have been developed for this application, as indicated by the prior art patents. The catalysts include copper/chrome, copper/silica, copper on kieselguhr, Raney copper, ion exchange copper on silica and copper on alumina catalysts. Most of the prior art catalysts used in this application have the problem of deactivation. The catalyst is deactivated by the accumulation of polyacrylamide on the surface or by the oxidation of surface copper. Selectivity is also important. Normally, hydration of Cxe2x80x94N bonds is favored by acidic oxides while hydrolysis of Cxe2x80x94C bonds is favored by basic oxides. Therefore, the surface acidity of the catalyst is crucial to this application.
For some other applications that require some surface basicity, alkaline metal or alkaline metal compounds should be remained or added to the catalyst matrix.
It is among the principal objects of the present invention to provide a non-chrome, copper-containing catalyst that can be employed as a catalyst in place of Cu/Cr catalysts in new or conventional chemical reactions.
It is another object of the present invention to provide a non-chrome, copper-containing catalyst that exhibits comparable or superior activity and selectivity to conventional Cu/Cr catalysts in a numerous chemical reactions.
Another object of the present invention is to provide a non-chrome, copper-containing catalyst having a spinel crystal structure analogous to the spinel crystal structure of conventional Cu/Cr catalysts.
Still another object of the invention to provide a non-chrome, copper-containing catalyst that contains an optimal ratio of copper to alumina. Yet another object of the present invention is to provide a non-chrome, copper-containing catalyst thereby eliminating the environmental issues associated with the disposal of chrome-containing catalysts.
A still further object of the invention is to provide a non-chrome, copper-containing catalyst that is relatively stable, and has a low percentage of leachable cations.
Still another object of the present invention is to provide a non-chrome, copper-containing catalyst that is efficient to prepare, functions well as a Cu/Cr catalyst in new or conventional chemical reactions, has good selectivity and is not easily deactivated.
In accordance with one aspect of the invention, a non-chrome, copper-based catalyst, Cuxe2x80x94Alxe2x80x94O, and a method of preparing the same are provided wherein the catalyst is prepared by co-precipitation from a solution consisting essentially of a soluble copper salt and a soluble aluminum compound in the presence of a precipitating agent. The copper salt is illustratively cupric nitrate, Cu(NO3)2, and the aluminum compound is preferably a basic aluminum salt, most preferably an aluminate such as sodium aluminate, Na2Al2O4. The copper salt and the aluminum compound are preferably dissolved separately and the solutions are slowly mixed in an aqueous precipitation mixture in approximately 5 minutes to 12 hours, more preferably in approximately 0.5 to 2 hours. The precipitant is preferably added to the precipitation mixture to maintain a pH of about 6.5 to 8.5, most preferably 7.4xc2x10.5. The precipitant is illustratively sodium carbonate, Na2CO3. The precipitate is filtered, washed to removed excess sodium, and dried, preferably at a temperature of from room temperature to about 150xc2x0 C., most preferably between about 100xc2x0 C. and 150xc2x0 C. The dried product is then calcined at a temperature ranging from about 300xc2x0 C. to about 1000xc2x0 C., the temperature of calcining being chosen to give the catalyst desired properties. The dried product, to be used in a powder form, is calcined at a preferred temperature of approximately 700xc2x0 C. to 900xc2x0 C. for approximately 0.5 to 4 hours. The dry powder, to be extrudated, after drying is then mixed with water to a desired water content. The dry powder, to be tableted, is calcined at a temperature of approximately 400xc2x0 C. to 700xc2x0 C.
The preferred catalysts of the present invention are generally homogeneous compositions having an aluminum content expressed as Al2O3 greater than about 20% by weight, preferably about 25% to about 70% by weight, and more preferably about 30% to about 60%. The copper content expressed as CuO is less than about 80% by weight, preferably about 40% to about 70% by weight. This convention is used throughout this patent, unless noted otherwise. The catalysts are generally homogeneous, rather than being supported by a heterologous matrix. The catalysts show a spinel structure when calcined above about 700xc2x0 C. Although the catalysts calcined at lower temperatures show no x-ray diffraction patterns characteristic of a spinel, and although they have different characteristics, such as higher leachable cations, they nonetheless show remarkable catalytic activity and selectivity in numerous reactions.
The Cuxe2x80x94Alxe2x80x94O catalyst produced by the method of the invention has been found to be comparable with or favorable to commercial Cu/Cr catalysts widely used in numerous hydrogenation and hydrogenolysis reactions, in terms of the most important characteristics of a commercial catalyst. In many reactions it has been found to have a far greater activity than commercially available Cu/Cr catalysts, and a remarkable selectivity. In extruded or tableted form, they have high side crush strength. They have high pore volumes, typically exceeding 0.25 ml/g. The powder form catalyst has high filtration rates. They resist poisoning. They have low cation extractability.
The solid catalyst formed as an extrudate of the catalyst of the present invention is preferably formed from a Cuxe2x80x94Alxe2x80x94O powder with LOD of thirty to fifty percent, the extrudate being formed with and without binder or lubricant. The extrudate has a pore volume of approximately 0.15 ml/mg to approximately 0.7 ml/g, preferably greater than 0.3 ml/g. The extrudate has a bulk density of approximately 0.6 g/ml to approximately 1.0 g/ml and a surface area of from 15 m2/g to 250 m2/g. The preferred extrudate has a bimodal pore size distribution centering around 100 xc3x85 and around 1000 xc3x85 to 2000 xc3x85.
When formed as a tablet, the catalyst has a pore volume greater than about 0.25 ml/g and a bulk density of approximately 0.8 g/ml to approximately 1.5 g/ml. The activity of the Cuxe2x80x94Alxe2x80x94O catalysts of the present invention can be increased in hydrogenolysis and other applications by the addition of promoters such as Ce, Mn, Ba, Zn, Co, and Ni compounds in amounts less than 50% by weight, preferably less than 25% by weight. In some applications the promoter is preferably less than 5% by weight, and most preferably between 0.1% and 2.5% by weight. The presence of alkaline metal compounds will improve selectivity in some applications.